Run Mode

The run mode has two conditions called Open Loop and Closed Loop.

When the engine is first started and engine speed is above 400 RPM, the system is in Open Loop operation. In Open Loop the PCM ignores the signal from the Heated Oxygen Sensor (HO2S), and calculates the air/fuel ratio based on inputs from the TP, ECT, and MAF sensors.

The system remains in Open Loop until the following conditions are met:
1. The HO2S has a varying voltage output showing that it is hot enough to operate properly (this depends on temperature).
2. The ECT has reached a specified temperature.
3. A specific amount of time has elapsed since starting the engine.

The specific values for the above conditions vary with different engines. When these conditions are met, the system enters Closed Loop operation. In Closed Loop the PCM changes fuel injector on-time based on the signal from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.